Answer:
Kc = 1.54e - 31 / 2.61e - 24
Step-by-step explanation:
 1 ) 
 ; Kc = 1.54e - 31
 ; Kc = 1.54e - 31
2) 
 ; Kc = 2.16e - 24
 ; Kc = 2.16e - 24
 upon reversing ( 2 ) equation
 
 Kc = 1/2.16e - 24
 Kc = 1/2.16e - 24 
 now adding 1 and reversed equation (2)
 

 

 we get ,
 
 Kc = 1.54e-31 × 1/2.61e - 24
 Kc = 1.54e-31 × 1/2.61e - 24
 equilibrium constant of equation (3) is -
 Kc = 1.54e - 31 / 2.61e - 24